Electric lamps



Feb. 20, 1962 D. P. COOPER, JR ELECTRIC LAMPS Filed Jan. 29, 1960 IN VEN TOR a A T'ORNEYS Uni ed S t s vPatat f "Q ice 3,022,437 ELECTRICLAMPS Dexter P. Cooper, Jr., Lexington, Mass., assignor to PolaroidCorporation, Cambridge, Mass., a corporation of Delaware Filed Jan. 29,1960, Ser. No. 5,525 3 Claims. (Cl. 313-218) This invention relates toelectric lamps and more particularly to new and improved electricincandescent lamps adapted to be operated at relatively hightemperatures and possessing relatively long, useful operating life atsuch high temperatures.

A principal object of the present invention is to provide inincandescent lamps of the character described at least one filamentcomprising tantalum carbide and at least one other metal carbideselected from the group consisting of the carbides of titanium, thorium,vanadium, niobium, molybdenum, tungsten and uranium, and a substantiallyoxygen-free atmosphere comprising, at operating temperatures, hydrogenand volatilized carbon.

Another object of the invention is to provide a filament comprisingtantalum carbide and a small amount of at least one other metal carbideselected from the group consisting of the carbides of titanium,thorium,lvanadium, niobium, molybdenum, tungsten and uranium which willnot sag appreciably at operating temperatures even after prolonged useand which will not readily break when' subjected to rough service suchas shocks, bumps, vibrations and the like.

Still another object of the invention is to provide a filament of theabove type for use in an atmosphere comprising, at operatingtemperatures, a halogen such as chlorine, hydrogen and volatilizedcarbon.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the products possessing thefeatures, properties and the relation of elements which are exemplifiedin the following detailed disclosure, and the scope of the applicationof which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing which is a representation of asection through a typical vehicle headlamp of the sealed-beam type.

There is a demand for incandescent lamps adapted to be operated atrelatively high filament temperatures and possessing relatively long,useful operating life as well as such properties as resistance to shock,vibration, sagging and the like. Such lamps would be desirable, forexample, in vehicle headlighting, in floodlighting for photographicpurposes, picture projection and the like. In vehicle headlamps, forinstance, the filament in order to withstand shock, vibrations and soforth must possess some flexibility, that is, it should not be brittleso as to readily break or disintegrate. However, the flexibility mustnot be such that sudden shock would bring the filament into contact withanother metallic part of the lamp and cause shorting. Moreover, thefilament should not be such that it appreciably sags at operatingtemperatures since such sagging increases the chances of shorting andpossibly of having an unsatisfactory positioning of the filament fromthe focus of the reflector.

This invention accordingly contemplates the use within a-lamp bulb orenvelope of a refractory or hard metal carbide filament of the typeheretofore described and an atmosphere the elements of which interactwith each other and with the described carbide filament in such a mannerthat the filament does not deteriorate over an extended period ofoperation at high filament temperatures.

The invention thus yields a lamp adapted for long operating life, roughservice and high efliciency.

The drawing illustrates a vehicle headlamp of the sealed-beam type whichcomprises a cup-shaped base member 10 having its inner surface 12silvered or otherwise coated to provide a metallic reflector, preferablyof paraboloidal shape. The base member has hermetically sealed thereto atransparent cover plate 14 of, for example, glass which may serve as alens element for controlling the dispersion of light emitted from thelamp. Within the bulb there is mounted or suspended a multicarbidefilament 16 on lead wires 18 which, in turn, are attached to subleads20. The subleads may be connected to a source of electric power outsidethe bulb or envelope. The multi-carbide filament is located at the focusof the reflector. After assembly, the bulb is evacuated and filled withan atmosphere which, at operating temperatures,

preferably comprises hydrogen, a halogen such as chlorine about 12 inchin length may be mounted on 40-mil leads.

within a standard T-20 envelope of about 270 cu. capacity,

into which about 2 cc. of carbon tetrachloride vapor and 20' cc. ofhydrogen, at atmospheric pressure and room temperature, have beenintroduced, along with sufiicient argon to bring the total pressurewithin the bulb to at least slightly less than one atmosphere.components may be cleaned and prepared in ways well known to the art. Itis desirable to coat the inner surface of the envelope (preferably afterthe formation of the reflector if such is used) with a material thatwill protect the envelope material, for example, glass, from attack.This may be done by evaporating calcium fluoride, for example, upon theinner surface of the envelope before the lamp is completely assembled.

The filaments of the present invention comprise tantalum carbide and atleast one other refractory metal carbide selected from the groupconsisting of the carbides of titanium, thorium, vanadium, niobium,molybdenum, tungsten and uranium. The multi-carbide filaments maycomprise solid solutions or mixtures of two refractory carbides such as,for example, tantalum carbide-titanium carbide, tantalum carbide-thoriumcarbide, tantalum carbide-niobium carbide, tantalum carbide-tungstencarbide, etc. Although-refractory metals such as, for example,molybdenum, tungsten, thorium, uranium, etc. are believed to form morethan one carbide, the preferred filaments will be considered as binarycarbide systems. The carbide filaments of the present invention comprisetantalum carbide and less than about 10 percent by weight of at leastone of the carbides of the refractory metals of groups IVa, Va and Vlaof the periodic chart or systern. Carbide filaments containing tantalumcarbide and amounts ranging from about 1 percent up to about 10 percentby weight of one or more of the previously mentioned refractory carbideshave been found to have increased flexibility and strength at elevatedtemperatures while substantially retaining other desirable propertiessuch as high melting points, thermal and electrical conductivities andthe like.

Although any convenient method of forming the carbide filaments may beused, it may be convenient to convert a filament comprising an alloy oftantalum and at least one of the preferred refractory metals to thecarbide structure after the bulb has been assembled. For example, thebulb may be constructed with all elements identical with those disclosedin the embodiment described above, except that the filament and leadsmay comprise an alloy of, for example, tantalum and tungsten; onespecific tantalum-tungsten alloy comprising about 7 per- Patented Feb.20,1962 W The bulb and cent of tungsten. The filament may then beconverted to the carbide form by passing suificient current through thefilament to yield a filament temperature of about 3100 C. In this way,the tantalum and tungsten, for example, comprising the filament and leadends associated with the filament will be substantially converted tocarbides.

The carbide filaments heretofore described may be of any suitableconfiguration, whether straight, coiled, crimped or otherwise shaped. Itshould also be noted that many materials may be used for leads. Forexample, the leads may be similar to the filament in composition or theymay be made of carbon, tungsten, platinum, palladium, rhodium, or asuitable metal clad or coated with, for example, platinum, palladium orrhodium.

The envelope atmosphere may comprise a volatile hydrocarbon and hydrogensuch as disclosed in US. Patent 2,596,469, or preferably the envelopeatmosphere may comprise, at operating temperatures, a halogen, hydrogenand a volatilized carbon. The preferred envelope atmosphere may beprovided by a number of materials or sources. For example, singlecompounds, such as ethylenediamine hydrochloride, methylaminehydrochloride and the like, are satisfactory. The necessary elements mayalso be provided by introducing into the envelope a combination ofmaterials, such as ethylene or another hydrocarbon and a gaseoushydrogen halide, for example hydrogen chloride; or a combination ofhydrogen, chlorine and any convenient hydrocarbon, for example methane,ethane, ethylene and the like; or a combination of hydrogen and anyconvenient halogenated hydrocarbon such as benzene hexachloride, thepolyhalogen derivatives of methane, ethane, etc., e.g., carbontetrachloride, tetrachloroethane and the like; or a combination ofhydrogen and poly-halogenated organic compounds such astetrachloroethylene and the like. It is obvious that the desiredatmosphere thus may be obtained in any number of suitable ways. Otherinert gases, such as xenon or krypton, may be used instead of argon.

Relatively high pressures within the bulb will lengthen lamp life; it isdesirable to maintain the pressure during operation at or near thehighest level that the envelope can safely withstand. If the pressuregenerated by the reacting gases is great enough, the need for an inertgas is reduced.

Other halogens may be used in place of chlorine without departing fromthe invention; members of the class of halogens having an atomic weightof less than 100, e.g., bromine and fluorine, are especially effective.If fluorine is used, however, precautions must be taken to avoiddecomposition of the bulb envelope and attack upon other lamp elements.If elemental halogens are used in preparing the lamp atmosphere,precautions should be taken to avoid inhalation or contact with the skinand eyes.

In general, any combination of materials may be used that will provide,at operating temperatures, an atmosphere of volatilized carbon andhydrogen and also, preferably, a suitable halogen, particularlychlorine, in the area surrounding the filament. The atmosphere should besubstantially free of water or oxygen; specifically, the oxygen contentshould be less than the order of fifty parts per million. The amount ofcarbon in the atmosphere should be sufficient to prevent the carbidefilament 4 from decomposing into free metal and carbon. Hydrogen andhalogen may be used in varying proportions; it is critical only thatenough hydrogen be present to prevent halogen from attacking the bulbcomponents, and that the total amount of hydrogen and halogen besufiicient to combine with the carbon atoms escaping from the regionsurrounding the filament to reduce to a minimum deposit of uncombinedcarbon upon the inner wall of the bulb or upon other exposed surfaces.Thus the atmosphere, at operating temperatures, preferably comprises anexcess by volume of hydrogen and halogen over vaporized carbon and anexcess by volume of hydrogen over halogen. For example, the employmentof benzene hexachloride produces an atmosphere comprising an atomicratio of approximately one carbon atom to one chlorine atom to sixhydrogen atoms. If the preferred atmosphere is provided by a mixture ofmaterials, such as a hydrocarbon and gaseous hydrogen chloride, adesirable atomic ratio is one carbon to three chlorine to five hydrogen.It is to be understood that these ratios may be varied widely, withinthe limits previously specified, without departing from the invention.

While the drawing particularly illustrates the applicability of thepresent invention to vehicle lamps, it is understood that the inventionmay be advantageously employed generally with incandescent lamps, forexample photoflood lamps and related structures adapted to projectcarefully controlled or substantially collirnated light beams.

Moreover, While the drawing describes a specific lamp configuration orstructure, it is understood that the 1ncandescent lamp may take anydesired shape and have any desired size. It may, for example, have anenvelope which is either transparent or translucent in whole or in partand, where a portion only of the envelope is light transmitting, theremainder may comprise a parabolic or other suitable reflector with thelamp filament positioned at the focus thereof.

Since certain changes may be made in the above products withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:

1. In an incandescent lamp, an atmosphere comprising, at operatingtemperatures, hydrogen and carbon, and a filament positioned within saidatmosphere comprising tantalum carbide and from about 1 to about 10% byWeight of at least one metal carbide selected from the group consistingof the carbides of titanium, thorium,

vanadium, niobium, molybdenum, tungsten and uranium.

2. A lamp according to claim 1 wherein the atmosphere also includes atleast one halogen.

3. A lamp according to claim 1 wherein the atmosphere also includes aninert gas of low heat conductivity.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN AN INCANDESCENT LAMP, AN ATMOSPHERE COMPRISING, AT OPERATINGTEMPERATURES, HYDROGEN AND CARBON, AND A FILAMENT POSITIONED WITHIN SAIDATMOSPHERE COMPRISING TANTALUM CARBIDE AND FROM ABOUT 1 TO ABOUT 10% BYWEIGHT OF AT LEAST ONE METAL CARBIDE SELECTED FROM THE GROUP CONSISTINGOF THE CARBIDES OF TITANIUM, THORIUM, VANADIUM, NIOBIUM, MOLYBDENUM,TUNGSTEN AND URANIUM.